The earphone has become a standard configured attachment of the terminal product. When the earphone is used, it usually requires that the terminal product automatically recognize the earphone plugging and unplugging state. Therefore, it needs to use the earphone plugging and unplugging detection circuit. The forms of the earphone plugging and unplugging detection circuit are various, and the spring leaf-type earphone plugging and unplugging detection circuit has the advantages of having simple circuit, low cost, and small area occupied by the Printed Circuit Board (PCB), and thus is widely used.
FIG. 1 is a schematic diagram of the definitions of the four-segment earphone plug and socket pin, and there are two types of four-segment earphone plugs: 3.5 mm and 2.5 mm, the definitions of the plug pins are: from the root to the end, ground (GND), microphone (MIC), right sound channel (R) and left sound channel (L). The three-segment earphone plug differs from the four-segment earphone plug in that the three-segment earphone plug does not have the MIC pin. The pins of the four-segment earphone socket pins are defined as comprising: the ground (GND) 1, the right sound channel 2 (R), the second pin 3 that forms a normally closed connection with the pin 2, the left sound channel 5 (L), and the first pin 4 that forms a normally closed connection with the pin 5, and the microphone 6 (MIC). The difference between the three-segment earphone socket and the four-segment earphone socket is that the three-segment earphone socket does not have the microphone (MIC) pin.
At present, a pair of mechanical spring leaves such as the pin 4 and the pin 5 that forms a normally closed connection with the pin 4 inside the earphone socket are used to implement the earphone plugging and unplugging detection. When the earphone is plugged in, the pin 5 is disconnected, and is electrically disconnected with the pin 4, thus an interruption is formed in the hardware and is reported to the control circuit, and the terminal equipment enables the interruption service routine. When the earphone is unplugged, the control circuit detects the earphone unplugging and exits from the service routine. The earphone plugging and unplugging makes the pin 4 connected and disconnected with the pin 5 of the earphone socket. Therefore, whether the state of earphone plugging and unplugging is able to be correctly detected is closely related to the mechanical spring leaves inside the earphone socket. When the earphone socket has a quality problem, for example, the pin 4 and the pin 5 should be normally closed but actually they are not, it will cause the controller to mistakenly judge that there are earphones plugged in, the earphone symbol appears in the terminal product, and meanwhile the audio path is switched to the earphone end, causing the entire terminal product to be in the silent mode, which seriously affects the normal use.